Cathode active material comprising additive for improving overdischarge-performance and lithium secondary battery using the same

a lithium secondary battery and active material technology, applied in the field can solve the problems of reducing the capacity affecting the performance of lithium secondary batteries, so as to achieve the effect of not significantly reducing the cell capacity

US20070015055A1Inactive Publication Date: 2007-01-18LG CHEM LTD
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Patent Information

Authority / Receiving Office
US · United States
Current Assignee / Owner
Publication Date
2007-01-18
Estimated Expiration
Not applicable · inactive patent

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Abstract

Disclosed is a cathode active material providing a cell performance that is not adversely affected by overdischarge, and a lithium secondary cell using the same. More particularly, the cathode active material for a lithium secondary cell comprises a lithium-transition metal oxide capable of lithium ion intercalation / deintercalation, wherein the cathode active material further comprises a lithium manganese oxide having a layered structure represented by the following formula 1 as an additive:[formula 1] LiMxMn1-x02 wherein, x is a number satisfying 0.05 x<0.5, and M is at least one metal selected from the group consisting of Cr, Al, Ni, Mn and Co. The lithium manganese oxide of formula 1 used as an additive for a cathode active material of a lithium secondary cell provides lithium ions in such an amount as to compensate for an irreversible lithium ion-consuming reaction at an anode, or more, thereby providing a lithium secondary cell which is low in capacity loss by over-discharge.
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Description

TECHNICAL FIELD

[0001] The present invention relates to a lithium secondary cell, the capacity of which is not significantly reduced after over-discharge and the capacity restorability of which after over-discharge is excellent, and more particularly, to a cathode active material comprising a lithium manganese oxide (LiMxMn1-xO2) having a layered structure as a cathode additive for improving over-discharge property, and a lithium secondary cell obtained by using the same. BACKGROUND ART

[0002] Recently, as mobile communication industries and information electronic industries progress in various technologies, a light-weight lithium secondary cell having a high capacity is increasingly in demand. However, a lithium secondary cell may ignite and explode due to extreme heat emission, when it is over-charged or is in a short circuit state. Moreover, when a lithium secondary cell is over-discharged below a normal voltage range, its capacity is rapidly reduced so that it may not be used an...

Examples

example 1

[0049] A pouch-type polymer cell of 383562 size was manufactured by a conventional method.

[0050] LiCoO2 was used as a cathode active material and LiCr0.1Mn0.9O2 was added in the amount of 8 parts by weight based on 100 parts by weight of the cathode active material.

[0051] LiCr0.1Mn0.9O2 was prepared by mixing lithium carbonate, manganese oxide and chrome oxide in solid phases, heat-treating the mixture at a temperature of 1000° C. under argon atmosphere for 12 hours, pulverizing the heat-treated mixture and further heat-treating the pulverized mixture at a temperature of 1100° C. under argon atmosphere for 12 hours.

[0052] Additionally, Super-p and PVDF polymer, used as a conductive agent and a binder, respectively, were added to NMP as a solvent to form cathode mixture slurry, and then the slurry was coated on an Al collector to obtain a cathode. On the other hand, artificial graphite and copper were used as an anode active material and an anode collector, respectively, and an EC...

experimental example 1

[0054]FIG. 3 is a graph showing the result of a structural analysis of the lithium manganese oxide, LiCr0.1Mn0.9O2, used as an additive for a cathode active material in Example 1 by X-ray diffraction. According to FIG. 3, it is apparent that the lithium manganese oxide of formula 1 is a compound having a layered structure.

[0055] On the other hand, as shown in FIG. 4, the lithium manganese oxide having a layered structure, LiCr0.1Mn0.9O2, was structurally changed into a spinel structure, after a coin-type cell obtained by using the same compound as an additive for a cathode active material experienced initial charge / discharge.

[0056] Additionally, as demonstrated in FIG. 5 showing the first charge / discharge capacity of a coin-type cell obtained by using the lithium manganese oxide of formula 1 having a layered structure as an additive for a cathode active material, the cell provided a very low first charge / discharge efficiency. As demonstrated in FIG. 6 showing the charge capacity a...

experimental example 2

[0057] A charge capacity and a discharge capacity before and after an over-discharge test were determined using each of the pouch-type polymer cells of 383562 size obtained from Example 1 and Comparative Example 1, through a conventional method. The over-discharge test results are shown in FIG. 8. Each of the numbers means a discharge capacity restorability at 0.2C and 1C after over-discharge, based on a discharge capacity at 0.2 C and 1 C before over-discharge. As shown in FIG. 8, Example 1 according to the present invention provided a discharge capacity restorability of 90% or more after an over-discharge test, and thus provided an excellent over-discharge preventing effect compared to Comparative Example 1.